Icing of an evaporator in a refrigeration circuit is a common problem. Vapor from ambient air condenses and freezes on the heat exchanging surfaces of the evaporator in the conventional cooling mode and forms a continuously increasing ice layer over the time. It is known that such ice layer reduces the efficiency of the heat transfer through the evaporator resulting in loss of efficiency and increase of operational costs of the refrigeration system.
A conventional evaporator comprises at least one conduit for directing the refrigerant through the evaporator and typically fins for increasing the heat exchange surface of the evaporator. The conduit frequently is a serpentine tube with a plurality of passes through the evaporator and the fins are plate like elements having openings through which the individual passes or sections of the tube extend. The fins and tube sections are fixed to each other, for example by means of a force fit and provide each other the required structural stability.
It is conventional to remove the ice accumulation on the evaporator by way of defrosting the evaporator. A typical method for defrosting is interrupting the normal cooling operations and to defrost the evaporator. It is possible to speed up the defrosting cycle by providing heat to the evaporator. In many applications, the temperature in the environment of the evaporator is critical. If, for example, the refrigeration circuit is part of a supermarket refrigeration system, the evaporators are typically within the display cabinets and a sudden temperature increase of the nutrition within such display cabinet during defrost operation should be avoided under all circumstances. The defrost operation should, therefore, be completed within a very short time, which requires the supply of a substantial amount of heat within a short time period. On the other hand, due to space requirement and economical reasons, any additional defrost apparatus should be avoided.